Error Analysis And Identification Of Lightweight Flexible Manipulator

Due to the high load-to-weight ratio, low power consumption, compact structure, and operation dexterity, lightweight manipulator has been widely used in the aerospace, anti-terrorism, EOD and family services. However, although a lot of advantages it bring, lightweight manipulator also have obvious defects, that is, low stiffness and the resulting error, which limits its application. In addition, the flexible error and geometric error are coupled together, greatly increasing the difficulty of error analysis and identification. The research object of this thesis is a typical lightweight manipulator with slender link, whose quality is also severely restricted. In order to make the error formation mechanism clear and improve the accuracy of the manipulator ultimately, this paper has conducted in-depth research in error modeling, identification and its compensation.A generalized error model with strong versatility is firstly derived based on the generalized pose error vector definition of frame. Because the DH method can not fully reflect the pose error of frame, the generalized geometric error of link coordinate system is derived by the introduction of modified DH law. and a generalized geometric error model of the manipulator is then proposed. The geometric error model can be used to guide the design of manipulator and help make error indicators. Then, a simulation example that analysis the geometric error of the end-effector is given.Flexibility is an important error source for lightweight manipulator, as well as makes it more difficult to analysis and identifies the error. In this thesis, the flexible joint is simplified to a linear torsion spring, while the link flexible deformation is analyzed based on the beam deformation theory, whereby the flexible error model of manipulator is established. According to the finite element simulation results, it is found that the flexible error model can reflect the error of manipulator accurately. Finally, a comprehensive error model for the lightweight manipulator is proposed by synthesizing the geometric error model and flexible error model and the error formation mechanism is clarified.Redundancy of the generalized error model will lead to a reduction in the accuracy of the error identification. After the linear combination of error Jacobian matrix column is got on the base of error sensitive matrix, a geometric error identification model whose redundancy is eliminated is obtained ultimately. Then, a certain number of sample points are selected for geometric error identification and the comprehensive error of them is measured. Next, the geometric error part of the end-effector is obtained by removing the flexible error part depend on flexible error model and geometric error identification is conducted. Simulation results show that identification model can accurately identify the mechanical DH parameters deviation of manipulator after the removal of redundancy.Finally, a feed forward compensation strategy is given and the simulation results show that the strategy is effective. The dynamic characteristic is also analyzed briefly and it is found that the effect of centrifugal force and the Coriolis force item on the joint torque can be neglected when the manipulator moves slowly. As a result, the proposed error model and compensation strategy can also be used to analyze and compensate the quasi-static error respectively.